The use of one transmission channel for several mobile telephone subscribers and/or mobile-telephone devices in order to increase the transmission capacity of a mobile telephone system is already known. Within this one transmission channel, a base station informs the mobile-telephone devices, which of the several mobile-telephone devices is in communication with the base station at which time.
For example, each transmission block, which is transmitted by the base station using an assignment signal, that is, a so-called “USF” (Uplink State Flag), specifies which of the mobile-telephone devices communicating with the base station in the same transmission channel can transmit to the base station during the next transmission block. A flexible assignment of this kind is described, for example, in published European Patent Application EP 1 139 614 Al. In this context, the transmission channel, which consists of a successive series of transmission blocks, is used by up to eight subscribers.
To ensure a smooth operation in such a system, which offers a considerable improvement in the exploitation of the transmission capacity of the transmission channel by comparison with a fixed assignment of a transmission channel to one subscriber, the assignment by the mobile-telephone devices must take place with a considerable degree of security. All such mobile-telephone devices are terminal devices, which communicate with the base station. In the event of a non-recognition of such an assignment signal by a mobile-telephone device, only a part of the potential transmission capacity remains unused; however, considerably greater difficulties arise in the event of an incorrect recognition by a mobile-telephone device. In the latter case, at least two mobile-telephone devices transmit simultaneously to the base station in a subsequent transmission block, and accordingly, the information communicated can, under some circumstances, no longer be evaluated.
In developing mobile-telephone devices and in developing the testing of devices in production, it is therefore necessary to determine the unrecognized assignments and to compare them with the total number of assignment signals received. For an error rate determined in this manner (BLER, Block Error Rate), a maximum-permissible limit of one percent has been established, for example, in the specification for an EGPRS system.